冷热与干湿循环作用下混凝土界面硫酸盐侵蚀损伤与演化机理

To date, the researches about the mechanism of sulfate attack on concrete are mainly based on the framework of phenomenological theory, which cannot reflect the intrinsic physical mechanism of micro-scale effect of damage in interfacial transition zone (ITZ). The present project starts with the interaction between composite configuration and ITZ, which is followed by the study of damage in concrete ITZ caused by sulfate attack and its evolution mechanism. The chemical analysis combined with modern phase measurement technology is adopted to research the rule of sulfate migration and crystallization in ITZ, and analyze the driving mechanism of diffusion-concentration-reaction/crystallization process of sulfate ion under the action of thermal-cooling and wet-dry cycles. With the ascertaining of interaction effect principle of thermal-cooling and wet-dry cycles on sulfate attack damage, the damage evolution process of ITZ micro-structure is simulated by 3D model. Through exploring the evolution law of mechanical behavior and reaming process of expansion cracks, the entire process model of sulfate attacked concrete under the action of thermal-cooling and wet-dry cycles is established. After that, the macro-failure rule of concrete is fitted, and the scale-span correlation of micro-structure damage evolution of ITZ, micro-mechanical behavior and macroscopic experimental mechanics can be achieved. Based on the former achievements and analysis of micro-scale effect of ITZ damage, the mechanism of concrete sulfate denudation subjected to thermal-cooling and wet-dry cycles will be revealed. The research results will be of great importance in improving the durability research and life prediction of road engineering structure.

目前关于混凝土硫酸盐侵蚀机理的研究主要建立在唯象理论基础之上，缺乏对其界面损伤微尺度效应内在物理机制的深刻描述。本项目从复合构型与界面之间的相互作用入手，对冷热与干湿循环作用下混凝土界面硫酸盐侵蚀损伤与演化机理展开研究：采用化学分析与现代物相测试技术相结合，研究界面区硫酸盐迁移与晶化规律，分析冷热与干湿循环作用对硫酸根离子扩散-浓缩-反应/结晶过程的驱动机制；探明冷热与干湿循环对界面硫酸盐侵蚀损伤的交互效应机理，三维重构界面微结构损伤演化过程；通过探究界面侵蚀力学行为演变与膨胀开裂扩孔过程，建立基于界面损伤的冷热与干湿循环作用下混凝土硫酸盐侵蚀劣化全过程模型，拟实其宏观失效规律，实现界面微结构损伤演化、微力学行为表征和宏观实验力学的跨尺度关联。综合上述成果，揭示基于界面损伤微尺度效应的冷热与干湿循环作用下混凝土硫酸盐剥蚀机理。研究成果对于完善道路工程结构耐久性研究与寿命预估具有重要意义。

目前国内外学者借助现代测试技术对混凝土在干湿循环作用下的硫酸盐侵蚀机理做了大量探索，但主要集中在宏观唯象研究。基于此，本项目从微尺度角度出发研究了冷热与干湿循环作用下混凝土界面硫酸盐侵蚀损伤与演化机理，其主要成果包括：结合实际应用情况，制备了不同强度等级混凝土以模拟冷热与干湿循环作用下的硫酸盐侵蚀特性，依据强度试验以及硫酸盐含量试验结果分析了强度劣化机理与侵蚀介质传输规律，结合Fick第二定律回归预测硫酸盐表观扩散系数与浓度时变机制，采用X射线衍射与原子力显微镜分析试验相结合，探究了界面过渡区在硫酸根侵蚀下晶体生成的驱动作用；模拟对比冷热与干湿循环作用下界面过渡区与水泥基体不同结构内部的硫酸盐微观迁移规律，基于CEMHYD3D模型和元胞自动机技术三维重构水泥基体与界面过渡区微结构，分析其形成和演化规律，并提取微结构数据于Matlab平台建立网络格构传输模型，设置不同边界条件并建立浓度扩散方程计算硫酸根离子扩散后生成浓度分布图，分析了界面过渡区与水泥基体在微观尺度上的结构和传输性能差异；为求解冷热与干湿循环下界面过渡区力学行为演变与膨胀开裂扩孔过程，基于混凝土硫酸盐侵蚀膨胀的弹塑性力学分析，采用圆筒形模型扩张理论进行混凝土内部集料外围的弹塑性区域半径、极限抗拉强度和塑性区域内各径向应力等计算求解，建立了基于界面损伤的混凝土膨胀开裂扩孔模型，揭示了混凝土界面过渡区在干湿循环作用下的硫酸盐剥蚀与膨胀破坏机理，实现了界面微结构损伤演化、微力学行为表征和宏观实验力学的跨尺度关联。研究成果对于丰富水泥混凝土硫酸盐侵蚀理论，完善道路工程结构耐久性研究与寿命预估具有重要意义。